Methods and systems for intracranial neurostimulation and/or sensing

ABSTRACT

Methods and systems for intracranial neurostimulation and/or sensing are disclosed. An intracranial signal transmission system in accordance with an embodiment of the invention includes a generally electrically insulating body having a head portion configured to be positioned at least proximate to an outer surface of a patient&#39;s skull, and a shaft portion configured to extend into an aperture in the patient&#39;s skull. The system can further include at least one electrical contact portion integrated with the support body. The at least one electrical contact portion can be positioned to transfer electrical signals to, from, or both to and from the patient&#39;s brain via an aperture in the patient&#39;s skull.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/891,834, filed Jul. 15, 2004, pending, which was acontinuation-in-part of U.S. application Ser. No. 10/418,796, filed Apr.18, 2003, now U.S. Pat. No. 7,302,298, which claims the benefit of U.S.Provisional Application No. 60/429,481, filed Nov. 27, 2002, which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to intracranial electrodes and methods forimplanting and using intracranial electrodes. These electrodes andmethods may be suited for neurostimulation systems and may also be usedin electroencephalography and other recording systems, e.g., evokedpotential recordings.

BACKGROUND

A wide variety of mental and physical processes are known to becontrolled or influenced by neural activity in the central andperipheral nervous systems. For example, the neural functions in someareas of the brain (e.g., the sensory or motor cortices) are organizedaccording to physical or cognitive functions. Several other areas of thebrain also appear to have distinct functions in most individuals. In themajority of people, for example, the areas of the occipital lobes relateto vision, the regions of the left inferior frontal lobes relate tolanguage, and the regions of the cerebral cortex appear to be involvedwith conscious awareness, memory, and intellect. Because of thelocation-specific functional organization of the brain, in which neuronsat discrete locations are statistically likely to control particularmental or physical functions in normal individuals, stimulating neuronsat selected locations of the central nervous system can be used toeffectuate changes in cognitive and/or motor functions throughout thebody.

In several existing applications, neural functions are treated byelectrical or magnetic stimulation powered by a neural stimulator thathas a plurality of therapy electrodes and a pulse system coupled to thetherapy electrodes. The therapy electrodes can be implanted into thepatient at a target site for stimulating the desired portions of thebrain. For example, one existing technique for masking pain in a patientis to apply an electrical stimulus to a target stimulation site of thebrain.

The brain can be stimulated in several known fashions. One type oftreatment is referred to as transcranial electrical stimulation (TES),which involves placing an electrode on the exterior of the patient'sscalp and delivering an electrical current to the brain through thescalp and the skull. TES, however, is not widely used because thedelivery of the electrical stimulation through the scalp and the skullcauses patients a great amount of pain and the electrical field isdifficult to direct or focus accurately.

Another type of treatment is transcranial magnetic stimulation (TMS),which involves using a high-powered magnetic field adjacent the exteriorof the scalp over an area of the cortex. TMS does not cause the painfulside effects of TES. Unfortunately, TMS is not presently effective fortreating many patients because the existing delivery systems are notpractical for applying stimulation over an adequate period of time. TMSsystems, for example, are relatively complex and require stimulationtreatments to be performed by a healthcare professional in a hospital orphysician's office. The efficacy of TMS in longer-term therapies may belimited because it is difficult to (a) accurately localize the region ofstimulation in a reproducible manner, (b) hold the device in the correctposition over the cranium for the requisite period, and (c) providestimulation for extended periods of time.

Another device for stimulating a region of the brain is disclosed byKing in U.S. Pat. No. 5,713,922, the entirety of which is incorporatedherein by reference. King discloses a device for cortical surfacestimulation having electrodes mounted on a paddle that is implantedunder the skull of the patient. These electrodes are placed in contactwith the surface of the cortex to create “paresthesia,” which is avibrating or buzzing sensation. Implanting the paddle typically requiresremoval of a relatively large (e.g., thumbnail-sized or larger) windowin the skull via a full craniotomy. Craniotomies are performed under ageneral anesthetic and subject the patient to increased chances ofinfection.

A physician may employ electroencephalography (EEG) to monitor neuralfunctions of a patient. Sometimes this is done alone, e.g., indiagnosing epileptic conditions, though it may also be used inconjunction with neurostimulation. Most commonly, electroencephalographyinvolves monitoring electrical activity of the brain, manifested aspotential differences at the scalp surfaces, using electrodes placed onthe scalp. The electrodes are typically coupled to anelectroencephalograph to generate an electroencephalogram. Diagnosis ofsome neurological diseases and disorders, e.g., epilepsy, may best beconducted by monitoring neural function over an extended period of time.For this reason, ambulatory electroencephalography (AEEG) monitoring isbecoming more popular. In AEEG applications, disc electrodes are appliedto the patient's scalp. The scalp with the attached electrodes may bewrapped in gauze and the lead wires attached to the electrodes may betaped to the patient's scalp to minimize the chance of displacement.

EEG conducted with scalp-positioned electrodes requires amplification ofthe signals detected by the electrodes. In some circumstances, it can bedifficult to pinpoint the origin of a particular signal because of thesignal dissipation attributable to the scalp and the skull. For moreprecise determinations, EEG may be conducted using “deep brain”electrodes. Such electrodes extend through the patient's scalp and skullto a target location within the patient's brain. Typically, these deepbrain electrodes comprise lengths of relatively thin wire that areadvanced through a bore through the patient's skull to the desiredlocation. If the electrodes are to be monitored over an extended periodof time, the electrodes typically are allowed to extend out of thepatient's skull and scalp and are coupled to the electroencephalographusing leads clipped or otherwise attached to the electrodes outside thescalp. To avoid shifting of the electrodes over time, the electrodestypically are taped down or held in place with a biocompatiblecementitious material. The patient's head typically must be wrapped ingauze to protect the exposed electrodes and the associated leads, andthe patient is uncomfortable during the procedure. This may be suitablefor limited testing purposes-deep brain encephalography typically islimited to tests conducted in hospital settings over a limited period oftime, usually no more than a few days—but could be problematic forlonger-term monitoring, particularly in nonclinical settings.

Screws have been used to attach plates or the like to patients' skulls.FIG. 1, for example, schematically illustrates a conventional cranialreconstruction to repair a fracture 50 or other trauma. In thisapplication, a plate 60 is attached to the outer cortex 12 of the skull10 by cortical bone screws 62. The plate 60 spans the fracture 50,helping fix the skull in place on opposite sides of the fracture 50. Ascan be seen in FIG. 1, the screws 62 do not extend through the entirethickness of the skull. Instead, the screws 62 are seated in the outercortex 12 and do not extend into the cancellous 18 or the inter cortex14. In some related applications, the screws 62 may be longer and extendinto or even through the cancellous 18. Physicians typically takesignificant care to ensure that the screws 62 do not extend through theentire thickness of the skull, though, because penetrating the skull canincrease the likelihood of trauma to or infection in the patient'sbrain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a conventional cranialreconstruction.

FIG. 2A is a schematic view in partial cross section of an intracranialelectrode in accordance with one embodiment of the invention implantedin a patient.

FIG. 2B is a schematic top elevation view of the implanted intracranialelectrode of FIG. 2A.

FIG. 3A is a schematic illustration in partial cross section of anintracranial electrode in accordance with another embodiment of theinvention implanted in a patient.

FIG. 3B is a schematic top elevation view of the implanted intracranialelectrode of FIG. 3A.

FIG. 4A is a schematic illustration in partial cross section of anintracranial electrode in accordance with yet another embodiment of theinvention implanted in a patient.

FIG. 4B is a side view of a dielectric member of the electrode of FIG.4A.

FIG. 5 is a schematic illustration in partial cross section of anintracranial electrode in accordance with still another embodiment ofthe invention implanted in a patient.

FIG. 6A is a schematic illustration in partial cross section of anintracranial electrode in accordance with a further embodiment of theinvention implanted in a patient.

FIG. 6B is a schematic top elevation view of the implanted intracranialelectrode of FIG. 6A.

FIG. 7 is a schematic illustration in partial cross section of anintracranial electrode in accordance with still another embodiment ofthe invention implanted in a patient.

FIG. 8 is a schematic side view of a broken-away portion of a patient'sskull in which an intracranial electrode in accordance with anotherembodiment of the invention has been implanted.

FIG. 9 is a schematic partial cross-sectional view taken along line 9-9of FIG. 8.

FIG. 10 is an isolation view of a portion of the implanted electrode ofFIG. 9.

FIG. 11 is a perspective view of selected components of the intracranialelectrode of FIGS. 8-10.

FIG. 12 is a schematic illustration in partial cross section of anintracranial electrode in accordance with yet another embodiment of theinvention implanted in a patient.

FIG. 13 is a schematic illustration in partial cross section of anintracranial electrode in accordance with one more embodiment of theinvention implanted in a patient.

FIG. 14 is a schematic illustration in partial cross section of anintracranial electrode in accordance with a further embodiment of theinvention implanted in a patient.

FIG. 15 is a schematic partial cross-sectional view of the intracranialelectrode of FIG. 13 with a retaining collar of the electrode in aradially compressed state.

FIG. 16 is a schematic partial cross-sectional view of the intracranialelectrode of FIG. 14 with the retaining collar in a radially expandedstate.

FIG. 17 is a schematic illustration in partial cross section of a deepbrain intracranial electrode in accordance with an alternativeembodiment of the invention implanted in a patient.

FIG. 18 is a schematic illustration in partial cross section of a deepbrain intracranial electrode in accordance with still another embodimentof the invention implanted in a patient.

FIG. 19 is a schematic overview of a neurostimulation system inaccordance with a further embodiment of the invention.

FIG. 20 is a schematic overview of a neurostimulation system inaccordance with another embodiment of the invention.

FIG. 21 is a schematic illustration of one pulse system suitable for usein the neurostimulation system of FIG. 17 or FIG. 18.

FIG. 22 is a schematic top view of the array of electrodes in FIG. 17.

FIGS. 23-26 are schematic top views of alternative electrode arrays inaccordance with other embodiments of the invention.

FIG. 27 is a schematic view in partial cross section of an intracranialelectrode implanted in a patient in accordance with another embodimentof the invention.

FIG. 28 is a schematic view in partial cross section of an intracranialelectrode implanted in a patient in accordance with another embodimentof the invention.

FIG. 29 is a schematic view in partial cross section of an intracranialelectrode implanted in a patient in accordance with another embodimentof the invention.

FIG. 30 is a schematic view in partial cross section of an intracranialelectrode having an adjunct depth-penetrating electrode implanted in apatient in accordance with another embodiment of the invention.

FIG. 31 is a schematic view in partial cross section of anotherintracranial electrode having an adjunct depth-penetrating electrodeimplanted in a patient in accordance with another embodiment of theinvention.

FIG. 32 is a schematic view in partial cross section of a neuralstimulation system implanted in a patient in accordance with analternative embodiment of the invention.

FIG. 33 is a schematic view in partial cross section of a neuralstimulation system implanted in a patient in accordance with yet anotherembodiment of the invention.

FIG. 34A is a schematic view in partial cross section of an intracranialelectrode system implanted in a patient in accordance with anotherembodiment of the invention.

FIG. 34B is a schematic illustration of an electrical energy transfermechanism in accordance with an embodiment of the invention.

FIG. 35 is a schematic view in partial cross section of portions ofintracranial electrode system implanted in a patient in accordance withan embodiment of the invention.

FIG. 36 is a schematic overview of an intracranial electrode systemimplanted in a patient in accordance with an embodiment of theinvention.

FIG. 37 is a schematic view in partial cross section of a set ofintracranial electrodes implanted in a patient in accordance with afurther embodiment of the invention.

FIG. 38 is a schematic view in partial cross section of an intracranialelectrode in accordance with a further embodiment of the invention.

FIG. 39 is a schematic view in partial cross section of an intracranialelectrode in accordance with an embodiment of the invention.

FIG. 40 is a schematic overview of an intracranial electrode systemhaving RFID capabilities in accordance with a further embodiment of theinvention.

FIG. 41 illustrates a depth measurement procedure employing a depthacquisition stick according to an embodiment of the present invention.

FIG. 42 is a flowchart illustrating depth measurement procedures inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION A. Overview

Various embodiments of the present invention provide intracranialelectrodes and methods for implanting and using intracranial electrodes.It will be appreciated that several of the details set forth below areprovided to describe the following embodiments in a manner sufficient toenable a person skilled in the art to make and use the disclosedembodiments. Several of the details and advantages described below,however, may not be necessary to practice certain embodiments of theinvention. Additionally, the invention can also include additionalembodiments that are not described in detail with respect to FIGS. 1-42.

One aspect of the invention is directed to an intracranial signaltransmission system that includes a generally electrically insulatingsupport body having a head portion configured to be positioned at leastproximate to an outer surface of a patient's skull. The support body canfurther have a shaft portion configured to extend into an aperture inthe patient's skull. At least one electrical contact portion is carriedby the support body and can be positioned to transfer electrical signalsto, from, or both to and from the patient's brain via the aperture inthe patient's skull.

An intracranial signal transmission system in accordance with anotheraspect of the invention includes an electrical contact portionconfigured to be positioned in an aperture of a patient's skull, and anelectrical energy transfer device configured to be releasably positionedexternal to the patient's scalp. The energy transfer device can becoupleable to a signal transmitter to transmit signals to the electricalcontact portion while the electrical contact portion is positionedbeneath the patient's scalp, and while the energy transfer device ispositioned external to the patient's scalp. In particular embodiments,the electrical energy transfer device can include a flexible outerlayer, an adhesive gel layer positioned to contact the patient's scalp,a conductive layer positioned between the outer layer and the adhesivegel layer, and a conductive lead connected to the conductive layer.

An intracranial signal transmission system in accordance with stillanother aspect of the invention includes a shaft configured to extendthrough an aperture in a patient's skull, and a head connected to theshaft. The head can be configured to be positioned adjacent to anexternal surface of the patient's skull and can be eccentricallypositioned relative to the shaft. Accordingly, the head can have a firstportion extending outwardly from the shaft by a first distance, and asecond portion extending outwardly from the shaft by a second distancedifferent from the first distance. The system can further include anelectrical contact portion carried by at least one of the shaft and thehead.

Other aspects of the invention are directed to methods for installingelectrodes and/or transmitting intracranial electrical signals. A methodin accordance with one aspect of the invention includes drilling a holein a patient's skull, and determining a distance from an outer surfaceof the patient's skull to a feature beneath the outer surface of thepatient's skull by inserting an elongated member having graduationmarkings into the pilot hole. The method can further include selecting asize of an intracranial electrode based on the distance determined withthe elongated member, and inserting the intracranial electrode into thehole. The method can still further include securing the intracranialelectrode to the patient's skull.

A method in accordance with another aspect of the invention includesforming an aperture in a patient's skull, with the aperture having afirst generally conical portion with a first diameter at an externalsurface of the patient's skull, and a second portion having a seconddiameter smaller than the first diameter, located beneath the externalsurface. The method can further include disposing proximate to theaperture an electrical contact portion carried by a support body havinga shaft and a head depending from the shaft. The head can have agenerally conical shape, with an angle between an external surface ofthe shaft and an external surface of the head being obtuse. The methodcan still further include inserting the support body into the apertureso that the shaft extends through the second portion of the aperture andthe head engages a wall of the aperture at the first portion of theaperture.

A method in accordance with yet another aspect of the invention includesforming an aperture in the patient's skull, disposing proximate to theaperture an electrical contact portion carried by a support body havinga shaft and a head depending from the shaft, with the shaft having anexternal surface and a plurality of surface features. The method canstill further include inserting the support body into the aperture sothat the shaft extends into the aperture, and then allowing thepatient's bone tissue to grow into interengagement with the surfacefeatures.

For ease of understanding, the following discussion is subdivided intothree areas of emphasis. The first section discusses certainintracranial electrodes; the second section relates to selectembodiments of neurostimulation systems; and the third section outlinesmethods in accordance with other embodiments of the invention.

B. Intracranial Electrodes

FIGS. 2-15 illustrate intracranial electrodes in accordance with variousembodiments of the invention. Like reference numbers are used throughoutthese figures to designate like or analogous elements.

FIGS. 2A-B illustrate an intracranial electrode 100 in accordance withone embodiment of the invention. This electrode 100 includes a head 102attached to a threaded shaft 110. The head 102 and shaft 110 may beintegrally formed of an electrically conductive material, e.g., titaniumor another biocompatible, electrical conductive metal. The head 102 mayinclude one or more slots 104, an alien head recess (not shown), orother structure (e.g., a square drive or TORX™ drive recess) adapted tofacilitate turning the electrode 100. As the electrode 100 is turned,the threads 112 of the threaded shaft 110 will advance a generallydistally positioned contact surface 115 of the electrode 100 toward thedura mater 20. The length of the shaft 110 may be selected so that thecontact surface 115 of the electrode 100 electrically engages thesurface of the dura mater 20 without causing undue harm to the duramater 20 or the underlying cerebral cortex. The contact surface 115 maycomprise a relatively blunt end to reduce trauma to the dura mater andthe underlying brain tissue 25.

In one embodiment, the intracranial electrode 100 is adapted to beelectrically connected to a pulse system (1050 in FIG. 18, for example),as described below. The electrode 100 may be connected to the pulsesystem in any desired fashion. In the illustrated embodiment, theelectrode 100 is coupled to such a pulse system by means of anelectrical lead 120. The electrical lead 120 shown in FIGS. 2A and 2Bcomprises an elongated, subcutaneously implantable body 124, which mayhave an insulative sheath. An electrically conductive ring or washer 122may be attached to an end of the body 124. In one embodiment, anopposite end of the body 124 is physically attached to a component ofthe pulse system. In other embodiments, the leads may be operativelyconnected to one or more components of the pulse system without beingphysically attached thereto, e.g., using a transmitter and antenna or amagnetic coupling. Embodiments of pulse systems incorporating suchwireless links are disclosed in U.S. Pat. No. 7,010,351, the entirety ofwhich is incorporated herein by reference.

The head 102 of the electrode 100 is adapted to be implantedsubcutaneously beneath the patient's scalp 30 (shown schematically inFIG. 2A). As explained below, the electrode 100 may be used to deliveran electrical signal to the brain tissue 25 adjacent the contact surface115. At higher stimulus levels, electrical contact between the patient'sscalp 30 and the head 102 of the electrode 100 may be uncomfortable forthe patient. If so desired, the scalp 30 may be electrically insulatedfrom the head 102. This may be accomplished by applying on the head 102a quantity of a dielectric, biocompatible, cementitious material (notshown), which may be cured or dried in place. In another embodiment, thehead 102 may be covered with a separate cap 130 (shown in dashed linesin FIG. 2A) formed of a dielectric material, e.g., a dielectric,biocompatible plastic, that may be glued, press-fit, or otherwiseattached to the head 102 and/or the lead 120.

The dimensions of the electrode 100 can be varied to meet various designobjectives. In one embodiment, however, the electrode 100 is longer thanthe thickness of the patient's skull. More specifically, the head 102 isadapted to be seated at an extracranial subcutaneous site while thethreaded shaft 110 is only slightly longer than the skull thickness atthe intended treatment site. Lengths on the order of 4-50 mm, forexample, may be appropriate in certain applications. The diameter of thehead 102 and the threaded shaft 110 may also be varied. For mostapplications, shafts 110 having diameters (typically excluding the widthof the threads 112) of no greater than 4 mm will suffice. Shaftdiameters of about 1-4 mm are likely, with diameters of 1.5-2.5 mm beingwell suited for most applications. FIGS. 2A-B illustrate an electrode100 having a constant diameter shaft 110, but it should be understoodthat the shaft diameter may vary. For example, the shaft 110 may taperdistally to improve the ability of the shaft 110 to be self-tapping. Thehead 102 typically will have a larger diameter than an adjoining portionof the shaft 110. (It should be recognized that FIGS. 2-15 are not drawnto scale. In particular, the aspect ratio of the electrodes issignificantly reduced to better illustrate certain functional aspects ofthe designs.)

FIG. 3A illustrates an intracranial electrode 150 in accordance withanother embodiment of the invention. This intracranial electrode 150 issimilar in many respects to the intracranial electrode 100 of FIGS.2A-B. For example, the electrode 150 includes an electrically conductivethreaded shaft 110 defining a blunt, atraumatic contact surface 115adjacent a distal end.

The connection of the electrode 150 to the lead 160 in FIGS. 3A-Bdiffers somewhat from the connection of the electrode 100 and lead 120in FIGS. 2A-B, however. In FIGS. 2A-B, the electrode 100 is electricallycoupled to the lead 120 by compressively engaging the electricallyconductive ring 122 of the lead 120 between the electrode head 102 andthe skull 10. In FIGS. 3A-B, the electrode 150 includes a head 152including slots 154 or other structure for engaging a screwdriver,wrench, or the like. The head 152 is adapted to engage a cap 162 carriedby the lead 160 that electrically couples the body 164 of the lead 160to the head 152 of the electrode 150. In the illustrated embodiment, thecap 162 comprises a dielectric body (e.g., a dielectric plastic materialwith some resilience) having an electrically conductive inner surface163, which may be provided by coating an interior surface of the cap 162with a metal. In one embodiment, the cap 162 is adapted to resilientlydeform to be press-fitted on the head 152. The body 164 of the lead 160may be coupled to the electrically conductive inner surface 163 of thecap 162, thereby providing an electrical pathway between the electrode150 and a pulse system (not shown) operatively coupled to the lead 160.

In one embodiment, the cap 162 is sized to be subcutaneously implantedbeneath the patient's scalp 30. In the illustrated embodiment, the head152 and the cap 162 both extend outwardly beyond the outer cortex 12 ofthe patient's skull 10. In another embodiment (discussed in more detailbelow with respect to FIGS. 38 and 39) some or all of the length of thehead 152 and/or the cap 162 may be countersunk into a recess formedthrough the outer cortex 12 and/or an outer portion of the cancellous18. This can improve patient comfort, which can be useful if theintracranial electrode 150 is intended to be implanted permanently orfor an extended period of time.

FIGS. 4A-B schematically illustrate aspects of an intracranial electrode200 in accordance with another embodiment. The electrode 200 maycomprise an electrically conductive inner portion 205 and anelectrically insulative outer portion 206. In the illustratedembodiment, the electrically conductive portion 205 of the electrode 200includes a head 202 and a threaded shaft 210 defining a contact surface215 for electrically contacting the patient's dura mater 20. Theseelements of the electrode 200 and their electrical connection to thelead 120 are directly analogous to the electrode 100 shown in FIGS.2A-B. The electrically insulative outer portion 206 of the electrode 200shown in FIG. 4A comprises a dielectric member 240 that is disposedbetween the threaded shaft 210 and the patient's skull 10. As shown inFIG. 4B, this dielectric member 240 may take the form of a taperedsleeve. The sleeve 240 may have an upper ring-like portion 242 and aplurality of deformable flanges 244 extending distally therefrom. Theflanges 244 may be adapted to be urged outwardly into compressivecontact with a bore formed in the patient's skull 10 when the threadedshaft 210 is advanced into the interior of the sleeve 240. Although notshown in FIG. 4B, ribs or teeth may be provided on the exterior surfacesof the flanges 244 to further anchor the sleeve 240 in the cancellous18. In one embodiment, the sleeve 240 is formed of a dielectric plasticand the threads of the threaded member 210 may be self-tapping in theinner wall of the sleeve 240.

When implanted in a skull 10 as shown in FIG. 4A, the dielectric sleeve240 will electrically insulate the skull 10 from the electricallyconductive shaft 210 of the electrode 200. (The sleeve 240 need notcompletely electrically isolate the skull and shaft 210; it merelyserves to reduce electrical conduction to the skull 10.) As explainedbelow, some embodiments of the invention employ an array comprising aplurality of intracranial electrodes implanted at various locations in apatient's skull 10. The use of a dielectric member such as thedielectric sleeve 240 can help electrically isolate each of theelectrodes 200 from other electrodes 200 in the array (not shown). If sodesired, the electrode 200 may be provided with a dielectric cap 230sized and shaped to be implanted subcutaneously beneath the patient'sscalp 30 (not shown in FIG. 4A). Much like the cap 130 of FIG. 2A, thiscap 230 may electrically insulate the patient's scalp from theelectrically conductive head 202. This may further improve electricalisolation of the electrodes 200 in an array.

FIG. 5 illustrates an intracranial electrode 250 in accordance with yetanother embodiment of the invention. This electrode 250 includes anelectrically conductive shaft 260 electrically coupled to asubcutaneously implantable head 262 and a distally positioned contactsurface 265. The shaft 260 is received in the interior of an externallythreaded dielectric layer 280. The shaft 260 may be operatively coupledto the dielectric layer 280 for rotation therewith as the electrode isthreadedly advanced through the patient's skull 10. In one embodiment,this may be accomplished by a spline connection between the shaft 260and the dielectric layer 280. In other embodiments, the dielectric layer280 may be molded or otherwise formed about the shaft 260.

In one particular embodiment, the dielectric layer 280 comprises anelectrically insulative ceramic material. In another embodiment, thedielectric layer 280 comprises an electrically insulative plastic orother biocompatible polymer that has sufficient structural integrity toadequately anchor the electrode 250 to the skull 10 for the duration ofits intended use. If so desired, the dielectric layer 280 may be porousor textured to promote osseointegration of long-term implants. Forshorter-term applications, the dielectric layer 280 may be formed of orcovered with a material that will limit osseointegration.

In at least some of the preceding embodiments, the intracranialelectrode 100, 150, 200, or 250 has a fixed length. In the embodimentshown in FIGS. 2A-B, for example, the distance between the base of thehead 102 and the contact surface 115 remains fixed. When the threadedshaft 110 is sunk into the skull 10 to a depth sufficient to compressthe conductive ring 122 of the lead 120 between the head 102 and theskull 10, this will also fix the distance from the exterior surface ofthe outer cortex 12 of the skull 10 to the contact surface 115. Thethickness of the skull 10 can vary from patient to patient and from siteto site on a given patient's skull. Hence, the pressure exerted by thecontact surface 115 against the dura mater 20 will vary depending on thethickness of the skull. If the electrode 100 is selected to be longenough to make adequate electrical contact with the dura mater adjacentthe thickest site on a skull, the pressure exerted by the contactsurface 115 against the dura mater 20 may cause undue damage at siteswhere the skull is thinner. Consequently, it can be advantageous toprovide a selection of electrode sizes from which the physician canchoose in selecting an electrode 100 for a particular site of a specificpatient's skull.

FIGS. 6-12 illustrate embodiments of electrodes with adjustable lengths.FIGS. 6A-B, for example, illustrate an intracranial electrode 300 thatis adapted to adjust a distance between the outer surface of the skull10 and a contact surface 315 of the electrode 300. This, in turn,enables the contact force between the contact surface 315 and thesurface of the dura mater 20 to be varied without requiring multipleelectrode lengths.

The intracranial electrode 300 of FIGS. 6A and 6B includes a probe orshaft 310 that has a blunt distal surface defining the contact surface315 of the electrode 300. The shaft 310 has a proximal end 312 that mayinclude a torque drive recess 314 or the like to facilitate rotation ofthe shaft 310 relative to a head 320 of the electrode 300. At least aportion of the length of the shaft 310 is externally threaded. In theillustrated embodiment, the shaft has an externally threaded proximallength and an unthreaded surface along a distal length.

The head 320 of the electrode 300 comprises a body 322 and a tubularlength 324 that extends from the body 322. The body 322 may be adaptedto be rotated by hand or by an installation tool. In one embodiment thebody 322 is generally hexagonal to facilitate rotation with anappropriately sized wrench. In the particular embodiment shown in FIGS.6A-B, the body 322 has a pair of recesses 323 in its outer face sizedand shaped to interface with a dedicated installation tool (not shown)having projections adapted to fit in the recesses 323. If so desired,the installation tool may be a torque wrench or other tool adapted tolimit the amount of torque an operator may apply to the head 320 of theelectrode 300 during installation. The tubular length 324 may beexternally threaded so the head 320 may be anchored to the skull 10 byscrewing the tubular length 324 into the skull 10.

The head 320 includes an internally threaded bore 326 that extendsthrough the thickness of the body 322 and the tubular length 324. Thebore 326 has threads sized to mate with the external threads on theshaft 310. If so desired, a biocompatible sealant (e.g., a length ofpolytetrafluoroethylene tape) may be provided between the threads of thebore 326 and the threads of the shaft 310 to limit passage of fluids orinfectious agents through the bore 326.

Rotation of the shaft 310 with respect to the head 320 will, therefore,selectively advance or retract the shaft 310 with respect to the head320. This will, in turn, increase or decrease, respectively, thedistance between the lower face 323 of the head body 322 and the contactsurface 315 of the shaft 310. As suggested in FIG. 6A, this may beaccomplished by inserting a tip 344 of a torque driver 340 into thetorque drive recess 314 in the shaft 310 and rotating the torque driver340. The tip 344 of the torque driver 340 may be specifically designedto fit the torque drive recess 314. In the embodiment shown in FIGS.6A-B, the torque drive recess 314 is generally triangular in shape andis adapted to receive a triangular tip 344 of the torque driver 340. Ifso desired, the torque driver 340 may comprise a torque wrench or thelike that will limit the maximum torque and operator can apply to theshaft 310 of the electrode 300.

If so desired, the torque driver 340 may include graduations 342 toinform the physician how far the shaft 310 has been advanced withrespect to the head 320. As noted below, in certain methods of theinvention, the thickness of the skull at the particular treatment sitemay be gauged before the electrode 300 is implanted. Using thisinformation and the graduations 342 on the torque driver 340, thephysician can fairly reliably select an appropriate length for theelectrode 300 to meet the conditions present at that particular site.

In the embodiment shown in FIGS. 6A-B, the head 320 and the shaft 310are both formed of an electrically conductive material. The conductivering 122 of the lead 120 may be received in a slot formed in the lowerface 323 of the body 322. Alternatively, the ring 122 may be internallythreaded, permitting it to be threaded over the external threads of thetubular length 324 before the head 320 is implanted. If so desired, thering 122 can instead be compressively engaged by the lower face 323 ofthe head 320 in a manner analogous to the engagement of the head 102with the ring 122 in FIG. 2A, for example.

In another embodiment, the head 320 is formed of a dielectric material,such as a dielectric ceramic or plastic. This may necessitate adifferent connection between the lead 120 and the shaft 310, such as byelectrically contacting the lead 120 to the proximal end 312 of theshaft 310. Employing a dielectric head 320 can help electricallyinsulate the skull 10 from the electrodes 300, improving signal qualityand reducing interference between the various electrodes 300 in anarray, as noted above.

FIG. 7 schematically illustrates an intracranial electrode 350 inaccordance with a further embodiment of the invention. The electrode 350includes a shaft or probe 360 having a proximal end 362 and a distallylocated contact surface 365. The shaft 360 may include a first threadedportion 360 a and a second threaded portion 360 c. In the embodimentshown in FIG. 7, the first and second threaded portions 360 a and 360 care separated by an unthreaded intermediate portion 360 b. In analternative embodiment, the two threaded portions 360 a and 360 cdirectly abut one another.

The intracranial electrode 350 of this embodiment also includes a head370 having an internally threaded bore 376 extending through itsthickness. The threads of the bore 376 are adapted to mate with thethreads of the first threaded portion 360 a. By rotating the shaft 360with respect to the head 370 (e.g., with a screwdriver 340), thedistance between the head 370 and the contact surface 365 can beadjusted in much the same manner described above in connection withFIGS. 6A-B.

The head 320 of the electrode 300 in FIGS. 6A-B has an externallythreaded tubular length 324 that extends into the skull 10 and helpsanchor the electrode 300 to the skull 10. The shaft 310 may then movewith respect to the skull by rotating the shaft 310 with respect to thehead 320. In the embodiment shown in FIG. 7, the head 370 is notdirectly anchored to the skull 10. Instead, the threads of the secondthreaded portion 360 c are adapted to threadedly engage the skull 10 toanchor the electrode 350 with respect to the skull 10 and the head 370is attached to the first threaded portion 360 a of the shaft 360. In oneembodiment, the shaft 360 may be threaded into a pilot hole in the skull10. Once the shaft 360 is positioned at the desired depth, the head 370may be screwed onto the first threaded portion 360 a of the shaft 360 tohelp fix the shaft 360 with respect to the skull and provide a lesstraumatic surface to engage the patient's scalp (not shown) when thescalp is closed over the electrode 350. In another embodiment, thelength of the electrode 350 may first be adjusted by rotating the shaft360 with respect to the head 370. Once the electrode 350 has the desiredlength, the shaft 360 may be advanced into the skull 10. The shaft 360may be graduated to facilitate adjustment to the appropriate length. Ifso desired, the first threaded portion 360 a may be threaded in adirection opposite the second threaded portion 360 c and/or the pitch ofthe threads in the first threaded portion 360 a may be different fromthe pitch of the threads in the second threaded portion 360 c.

In the embodiment of FIG. 7, the shaft 360 of the electrode 350 extendsthrough the dura mater 20 and the contact surface 365 of the electrode350 is in direct contact with the cerebral cortex of the patient'sbrain. This is simply intended to illustrate one alternativeapplication. In other embodiments, the length of the electrode 350 maybe selected so that the contact surface 365 electrically contacts thedura mater 20 without extending therethrough, much as illustrated inFIG. 6A, for example.

FIGS. 8-11 illustrate an intracranial electrode 400 in accordance withanother embodiment of the invention. The intracranial electrode 400includes a shaft or probe 410 that is slidably received by a head 420.The shaft 410 comprises an electrically conductive material and definesan electrical contact surface 415, e.g., on its distal end.

In the preceding embodiments, some or a majority of the head of theelectrode extends outwardly beyond the outer surface of the skull 10. Inthe particular implementation shown in FIGS. 8-10, the head 420 isreceived entirely within the thickness of the skull 10. It should beunderstood, though, that this is not necessary for operation of thedevice, and this is shown simply to highlight that the position of thehead 420 with respect to the skull 10 can be varied. In anotherembodiment, at least a portion of the head 420 extends outwardly beyondthe outer surface of the skull 10.

The head 420 includes a base 430 and an actuator 422. The base 430includes an externally threaded body 432 and a tubular length 434 thatextends from the body 432. A portion of the tubular length 434 carriesexternal threads 436. The tubular length 434 may also include one ormore locking tabs 440, each of which includes an actuating surface 442.

The actuator 422 has an internally threaded bore 424 that is adapted tomatingly engage the threads 436 on the base 430. Rotating the actuator422 with respect to the base 430 in a first direction will advance theactuator 422 toward the actuating surface 442 of each of the tabs 440.The actuator 422 may urge against the actuating surfaces 442, pushingthe tabs 440 inwardly into engagement with the shaft 410. This will helplock the shaft 410 in place with respect to the base 430. Rotating theactuator 422 in the opposite direction will allow the tabs 440 toresiliently return toward a rest position wherein they do not brakemovement of the shaft 410. The force with which the shaft 410 engagesthe dura mater 20 (not shown) then can be adjusted to a desired level bymoving the shaft 410 with respect to the base 430. When the shaft 410 isin the desired position, the actuator 422 may be moved into engagementwith the tabs 440 to hold the shaft 410 in the desired position.

FIG. 12 illustrates an adjustable-length intracranial electrode 450 inaccordance with another embodiment. The intracranial electrode 450includes an axially slidable probe or shaft 452 and a head 460. The head460 includes a body 462 and an externally threaded tubular length 464.The tubular length 464 includes an axially extending recess 466 sized toslidably receive a portion of the shaft 452. An O-ring 465 or the likemay provide a sliding seal between the head 460 and the shaft 452.

The contact surface 455 of the shaft 452 is pushed against the surfaceof the dura mater 20 with a predictable force by means of a spring 454received in the recess 466. In FIG. 12, the spring 454 is typified as acompressed coil spring formed of a helically wound wire or the like. Inthis embodiment, an electrical contact 469 of the lead 468 may beelectrically coupled to the wire of the spring 454. Electrical potentialmay then be conducted to the shaft 452 by the wire of the spring 454.

In another embodiment (not shown), the spring 454 comprises a compressedelastomer, which may take the form of a column that fills some or all ofthe diameter of the recess 466. The elastomer may comprise abiocompatible polymeric material, for example. In such an embodiment,the elastomer may be electrically conductive, e.g., by filling apolymeric material with a suitable quantity of a conductive metal powderor the like. In another embodiment, one or more wires may be embedded inthe elastomeric material to conduct an electrical signal across theelastomer to the shaft 452.

In the illustrated embodiment and the alternative embodiment wherein thespring 454 comprises an elastomer, the head 460 may be formed of adielectric material, helping electrically insulate the skull 10 from theshaft 452. In an alternative embodiment, the head 460 may be formed ofan electrically conductive material. Even though the other structuralelements of the electrode 450 may remain largely the same, this wouldavoid the necessity of having the lead 468 extend through the head 460;an electrically conducive ring 122 or the like instead may be employedin a manner analogous to that shown in FIG. 6A, for example.

FIG. 13 depicts and adjustable-length intracranial electrode 475 inaccordance with a different embodiment. Some aspects of the intracranialelectrode 475 are similar to the intracranial electrode 450 shown inFIG. 12. In particular, the intracranial electrode 475 includes anaxially slidable probe or shaft 480 that is slidably received in anaxially extending recess 488 in a tubular length 492 of a head 490. Aproximal face of the body 490 may include a pair of tool-receivingrecesses 494, which may be analogous to the tool-receiving recesses 323noted above in connection with FIG. 6A, to aid in the installation ofthe body 490. If so desired, one or more seals may be provided betweenthe shaft 480 and the body 490. In the embodiment shown in FIG. 13, thebody 490 carries a first O-ring 493 and the shaft 480 and carries asecond O-ring 484 sealed against the interior of the recess 488. TheseO-rings may also serve as abutments to limit axial travel of the shaft480 in the recess 488.

The contact surface 481 of the shaft 480 is pushed against the surfaceof the dura mater 20 with a predictable force by means of a spring 486.The spring 486 may be substantially the same as the spring 454 shown inFIG. 12, and the various materials suggested above for the spring 454may also be employed in the spring 486 of FIG. 13.

In FIG. 12, the spring 454 provides the electrical connection betweenthe lead 468 and the shaft 452. In the embodiment of FIG. 13, however,the lead 496 may be connected directly to the shaft 480 through a lumen495 in the body 490. This lumen 495 is sized to slidably receive areduced-diameter neck 482 of the shaft 480. As the body 490 is screwedinto the skull 10 and moves toward the brain 25, contact between theshaft 480 and the dura mater 20 will urge the shaft 480 upwardly, movingthe neck 482 upwardly within the lumen 495.

The electrode 475 of FIG. 13 may facilitate delivering a highlyreproducible contact force of the contact surface 481 of the shaft 480against the dura mater 20. The position of the reduced-diameter neck 482of the shaft 480 within the lumen 495 will vary in a fixed relationshipwith the force exerted on the spring 486 by the shaft 480. Since theforce of the shaft 480 against the spring 486 is essentially the same asthe force of the shaft 480 against the dura mater 20, knowing theposition of the neck 482 within the lumen 495 can give the operator anindication of the force exerted against the dura mater 20. In oneparticular embodiment, the interior of the lumen 495 may be graduated tomark off the depth of the neck 482 in the lumen 495. In anotherembodiment, the body 490 may be driven into the skull 10 until theheight of the neck 482 in the lumen 495 reaches a predetermined point,e.g., when the top of the neck 482 is flush with the top of the body490.

FIG. 14 illustrates an intracranial electrode 500 in accordance withstill another embodiment of the invention. This electrode 500 includesan electrically conductive probe or shaft 510 having a head 512 and acontact surface 515. A radially compressible retaining collar 540extends along a portion of the length of the shaft 510. As shown in FIG.15, the retaining collar 540 may be adapted to assume a radially reducedconfiguration in response to a compressive force, indicatedschematically by the arrows F. This compressive force F may be generatedby collapsing the retaining collar 540 and restraining it in the lumenof an introducing sheath (not shown) sized to be received in a borethrough the skull 10. When this force F is removed (e.g., by retractingthe introducing sheath), the retaining collar 540 may expand radiallyoutwardly away from the shaft 510, as illustrated in FIG. 16.

To implant the electrode 500 in the skull 10, the shaft 510 may beadvanced into a bore in the skull until the contact surface 515 exertsthe desired contact force against the dura mater 20. Once the shaft 510is in the desired position, the compressive force F on the collar 540may be released, allowing the collar 540 to expand outwardly intocompressive engagement with the lumen of the bore in the skull 10. Thiswill help hold the electrode 500 in place with respect to the skullwithout requiring permanent anchoring of the shaft 510 to the skull 10.

The shaft 510 may be electrically coupled to a pulse system (not shown)by a lead 520. The lead 520 may include a cap 522 having an electricallyconductive inner surface 524 coupled to a body 526 of the lead. The lead520 may be analogous to the lead 160 shown in FIGS. 3A-B. Any othersuitable electrical connection between the shaft 510 and the pulsesystem may be employed.

In one embodiment, the collar 540 comprises a dielectric material. Thiswill help electrically insulate the skull 10 from the shaft 510. Inanother embodiment, the collar 540 is electrically conductive and thelead 520 may be electrically coupled to the shaft 510 via the collar540.

In the embodiment shown in FIG. 14, the shaft 510 may have a length onlya little longer than the thickness of the patient's skull 10 and thecontact surface 515 may be relatively blunt. Such a design is useful forrelatively atraumatic contact with the dura mater 20. In anotherembodiment suggested in dashed lines in FIGS. 15 and 16, the electrode500 may instead have a substantially longer shaft 510 a and a relativelysharp contact surface 515 a. Such an embodiment may be useful fordirectly stimulating a particular location within the cerebral cortex orsome other location within the deeper tissues of the brain.

FIG. 17 schematically illustrates how certain principles of theinvention can be embodied in a subcortical or deep brain intracranialelectrode 550. The electrode 550 generally includes a threaded shaft 560having a head 562. The head 562 may be coupled to a pulse system or asensing unit (as described below) via a lead 160 in the same manner lead160 is attached to the head 152 of electrode 150 in FIGS. 3A-B. (Likereference numbers are used in these figures to indicate like elements.)The electrode 550 also includes an elongate conductive member 570 thatextends inwardly from the skull 10 to a selected target site 28. Theconductive member 570, which may comprise a length of a conductive wire,may be electrically shielded by a dielectric sheath along much of itslength and have an exposed, electrically conductive tip 574.

In use, the conductive member 570 may be slid freely through a pilothole 11 formed through the skull to position the tip 574 at the targetsite 28 in a known manner. The pilot hole 11 may be larger than theconductive member 570 or be tapped to receive the threads of the shaft560. With the conductive member 570 in place, the shaft 560 may bethreaded into the pilot hole 11, crimping the conductive member 570against an interior of the pilot hole 11. This will fix the conductivemember 570 in place. If so desired, a proximal length 572 of theconductive member 570 may extend outwardly of the skull and be held inplace by the head 562. The threads of the threaded shaft 560 may alsocut through the dielectric sheath of the conductive member 570 as theshaft 560 is screwed into place, making electrical contact with theconductive wire therein.

FIG. 18 schematically illustrates a subcortical or deep brainintracranial electrode 600 in accordance with an alternative embodimentof the invention. This electrode 600 includes a head 610 having athreaded shaft 620 with an axially-extending opening 622 extendingthrough the length of the head 610. The head 610 may also include agimbal fitting 630 adapted to slidably receive a length of a conductivemember, which may comprise the same type of elongate conductive member570 discussed above in connection with FIG. 17.

The gimbal fitting 630 is adapted to allow an operator greater controlover the placement of the electrically conductive tip 574 of theconductive member 570. In use, the tip 574 of the conductive member 570will be threaded through an opening in the gimbal fitting 630. Bypivoting the gimbal fitting 630 with respect to the threaded shaft 620of the head 610, the angular orientation of the conductive member 570with respect to the pilot hole 11 in the skull 10 can be accuratelycontrolled. Once the operator determines that the conductive member 570is at the appropriate angle, e.g., using a surgical navigation systemsuch as that noted below, the operator may advance the conductive member570 to position the conductive tip 574 at the target site 28. Once thetip 574 is in position, the cap 162 of a lead 160 may be press-fitted onthe body 610 of the electrode 600. This will crimp the proximal length572 of the connective member 570 between the body 610 and the conductiveinner surface 163 of the cap 162, providing an effective electricalconnection between the conductive member 570 and the body 164 of thelead 160.

FIGS. 27-29 schematically illustrate intracranial electrodes that formportions of signal transmission systems in accordance with furtherembodiments of the invention. In FIG. 27, an electrode 700 comprises abody (e.g., a support body) that includes a head 702 coupled to a shaft710. The body of the electrode 700 may be integrally formed of anelectrically conductive inner core 708 clad with a biocompatibleelectrically insulating material 712. In the illustrated embodiment, theelectrically conductive portion 708 of the electrode 700 extends alongthe length of both the head 702 and the shaft 710. An electrical lead720 may be coupled to the electrode core 708 to facilitate electricalsignal transfer, for example, for electrical stimulation and/ormonitoring. In certain embodiments, the lead 720 may be coupled to apulse generator. An electrical contact or contact portion 704 transmitselectrical signals to and/or from the brain tissue 25. The electricalcontact portion 704 can be integral with or connected to the conductiveinner core 708. In the particular embodiments shown in FIGS. 27-29, theelectrical contact portions are housed within an insulative body.Electrical contact portions in accordance with other embodiments of theinvention can have other arrangements (e.g., they can form part of alarger, generally conductive element).

FIG. 28 illustrates another intracranial electrode 750 in accordancewith an embodiment of the invention. In this embodiment, the body ofelectrode 750 may comprise a biocompatible electrically insulatingmaterial 765 containing a set of biocompatible, electrically conductivecontacts 760 a and 760 b. The electrically conductive contacts 760 a and760 b may be carried by different portions of the electrode 750 tofacilitate production of particular types of electric fielddistributions. In one embodiment, a first contact 760 a may be carriedby the head 762, and a second contact 760 b may be carried by a distalportion of the shaft 755, which may be configured to be in electricalcontact with a stimulation site. A lead 770 may comprise lead wires orlinks 772 and 774 to provide electrical signal pathways to the contacts760 a and 760 b.

FIG. 29 illustrates yet another embodiment of an intracranial electrode780. In the embodiment shown, the intracranial electrode 780 maycomprise electrical contacts 796 and 798 that are carried by a distalportion of a shaft 785. A head 782 can stabilize the shaft 785 relativeto the skull 10. A lead 790 may comprise lead wires or links 792 and 794that are electrically coupled to one or more contacts 796 and 798. Suchlead wires 792 and 794 may facilitate electrical stimulation and/ormonitoring using one or both contacts 796 and 798.

In an embodiment shown in FIG. 29, the shaft 785 can carry two contacts796, 798, and in other embodiments, the shaft 785 can carry more orfewer contacts. The diameter of the shaft 785 can be selected based onfactors that include the number of contacts carried by the shaft 785. Inparticular embodiments, the shaft 785 can have a diameter of from about0.5 millimeters to about 3.0 centimeters. In other embodiments, thediameter of the shaft 785 can have other values. The shaft 785 can beinserted into the skull in a manner that is consistent with the diameterof the shaft 785. For example, smaller shafts 785 can be insertedthrough a burr hole in the skull 10, and larger shafts 785 can beinserted using a craniotomy procedure.

FIGS. 30 and 31 schematically illustrate other embodiments of theinvention that may be applicable to cortical, subcortical, and/or deepbrain stimulation and/or monitoring situations. Such embodiments mayfacilitate stimulation and/or monitoring involving surface or corticaltissues and/or subcortical or deep brain tissues. In FIGS. 30 and 31,like reference numbers may correspond to identical, essentiallyidentical, or analogous elements. One embodiment of a combinedintracranial electrode assembly 800 is shown in FIG. 30. The combinedintracranial electrode assembly 800 comprises a first electrode 810 anda second electrode 820. The first and second electrodes 810 and 820 maybe configured and dimensioned for placement relative to physicallydistinct locations of the brain. For example, the first electrode 810may be in contact with the dura 20, while the second electrode 820 maybe positioned relative to a subcortical or deep brain location.

In one embodiment, the first electrode 810 comprises at least oneelectrical contact 815 carried by a distal portion of a shaft 816. Afirst lead wire 830 may be coupled to the first electrode's contact 815.The second electrode 820 may comprise an elongate member 822 thatcarries one or more conductive portions, sections, segments, and/orcontacts 825, in a manner identical, essentially identical, or analogousto that described above. A second lead wire 835 may be coupled to thesecond electrode's contact(s) 825. The length of the second electrode820, the position of one or more contacts 825 carried by the secondelectrode 820, and/or the particular contacts 825 that are electricallyactive at any given time may depend upon a targeted tissue type orlocation and/or establishment of a desired type of stimulation and/ormonitoring configuration. In one embodiment, each electrode 810, 820 canprovide independently controlled stimulation signals. In anotherembodiment, one of the electrodes 810, 820 can be coupled to atransmitter to provide stimulation signals to the patient, and the othercan be coupled to a sensor to receive diagnostic signals from thepatient. The electrodes 810, 820 can be coupled to a common ground, orcan be coupled to independent grounds.

FIG. 31 illustrates an embodiment of an intracranial electrode assembly800 wherein a first electrode 810 comprises at least one electricalcontact 817 carried by a head 812. Although the contact 817 is shownspanning a proximal surface portion of the head 812, it is to beappreciated that the contact 817 may be located along, upon, and/orwithin various portions of the head 812. In one embodiment, the firstelectrode 810 comprises a shaft 816 that need not touch or rest againstneural tissue such as the dura 20. Rather, the shaft 816 may be shorterthan in an embodiment such as shown in FIG. 30. In another embodiment, afirst electrode 810 may include a contact 815 (FIG. 30) carried by theshaft 816 in addition to the contact 817 carried by the head 812. Suchan embodiment may include an additional lead wire (not shown).

In a manner identical, essentially identical, or analogous to otherembodiments described herein, a combined electrode assembly 800 may becomprised of one or more electrically nonconductive portions along withone or more electrically conductive portions. In one embodiment,nonconductive portions 814 and 822 of the first and second electrodes810 and 820, respectively, may be formed from one or more biocompatiblematerials (e.g., plastic, silicone, and/or other materials), andconductive portions such as the first and second sets of contacts 815and 825 may be formed from one or more biocompatible conductivematerials (e.g., Titanium, Platinum, and/or other materials).

Through appropriate electrical coupling, for example, by way of leads830 and 835, to an electrical source such as a pulse generator, one ormore contacts 815 may be configured as an anode or a cathode, whileother contacts 825 may respectively be configured as a cathode or ananode to facilitate bipolar and/or unipolar stimulation as furtherdescribed below. For example, a combined electrode assembly 800 may beimplanted into a patient such that a local contact portion, which maycomprise a distal portion of a shaft 816, resides at, upon, or proximateto a stimulation site; while a remote contact portion, which maycomprise a distal portion 826 of an elongate member 822, provides aremote or distant circuit completion site.

In general, the applicability of one or more intracranial electrodeembodiments to any given neural stimulation and/or monitoring situationmay depend upon the location, depth, and/or spatial boundaries of targetneural structures and/or target neural populations under consideration,which may depend upon the nature of a patient's neurological conditionor disorder. The extent to which an electric field reaches, penetrates,and/or travels into and/or through target neural structures and/or atarget neural population may affect neural stimulation efficiency and/orefficacy. Various intracranial electrode embodiments in accordance withthe invention, for example, those described above with reference toFIGS. 27-31, may have conducting portions in various positions orlocations, which may facilitate establishment of particular types ofelectric field distributions at one or more times.

C. Systems Employing Intracranial Electrodes

FIG. 19 is a schematic illustration of a neurostimulation system 1000 inaccordance with one embodiment of the invention. This neurostimulationsystem 1000 includes an array 1010 of intracranial electrodes and aninternally implantable pulse system 1050. The array 1010 of electrodesmay employ one or more electrodes in accordance with any one or more ofthe embodiments described above in connection with FIGS. 2-18 and/or27-31 and/or any other suitable design. In the particular implementationdepicted in FIG. 19, the array 1010 (shown schematically in FIG. 20)includes a first implantable intracranial electrode 100 a and a secondimplantable intracranial electrode 100 b, each of which may besubstantially the same as the electrode 100 shown in FIGS. 2A-B. Theseelectrodes 100 b and 100 b extend through the skull 10 into contact withthe dura mater 20 at two spaced-apart locations.

The pulse system 1050 may be implanted in the body of the patient P at alocation remote from the array 1010 of electrodes 100. In the embodimentshown in FIG. 19, the pulse system 1050 is adapted to be implantedsubclavicularly. In the alternative embodiment shown in FIG. 20, thepulse system 1050 is adapted to be implanted in a recess formed in thepatient's skull 10. In either embodiment, each of the electrodes 100 inthe array 1010 is electrically coupled to the pulse system 1050 by meansof a separate lead (120 in FIGS. 2A-B) having an elongate,subcutaneously implantable body 124. Hence, electrode 100 a is coupledto the pulse system 1050 by the elongate body 124 a of a first lead andthe other electrode 100 b is coupled to the pulse system 1050 by theelongate body 124 b of another lead. In one embodiment, the elongatebodies 124 a-b are combined into a single subcutaneously implantablecable or ribbon.

FIG. 21 schematically illustrates one pulse system 1050 suitable for usein the neurostimulation system 1000 shown in FIG. 19. The pulse system1050 generally includes a power supply 1055, an integrated controller1060, a pulse generator 1065, and a pulse transmitter 1070. The powersupply 1055 can be a primary battery, such as a rechargeable battery orother suitable device for storing electrical energy. In alternativeembodiments, the power supply 1055 can be an RF transducer or a magnetictransducer that receives broadcast energy emitted from an external powersource and converts the broadcast energy into power for the electricalcomponents of the pulse system 1050.

In one embodiment, the controller 1060 includes a processor, a memory,and a programmable computer medium. The controller 1060, for example,can be a computer, and the programmable computer medium can be softwareloaded into the memory of the computer and/or hardware that performs therequisite control functions. In an alternative embodiment suggested bydashed lines in FIG. 21, the controller 1060 may include an integratedRF or magnetic controller 1064 that communicates with an externalcontroller 1062 via an RF or magnetic link. In such a circumstance, manyof the functions of the controller 1060 may be resident in the externalcontroller 1062 and the integrated portion 1064 of the controller 1060may comprise a wireless communication system.

The controller 1060 is operatively coupled to and provides controlsignals to the pulse generator 1065, which may include a plurality ofchannels that send appropriate electrical pulses to the pulsetransmitter 1070. The pulse generator 1065 may have N channels, with atleast one channel associated with each of N electrodes 100 in the array1010. The pulse generator 1065 sends appropriate electrical pulses tothe pulse transmitter 1070, which is coupled to a plurality ofelectrodes 1080. In one embodiment, each of these electrodes is adaptedto be physically connected to the body 124 of a separate lead, allowingeach electrode 1080 to electrically communicate with a single electrode100 in the array 1010 on a dedicated channel of the pulse generator1065. Suitable components for the power supply 1055, the integratedcontroller 1060, the pulse generator 1065, and the pulse transmitter1070 are known to persons skilled in the art of implantable medicaldevices.

As shown in FIG. 20, the array 1010 of electrodes 100 in FIG. 19comprises a simple pair of electrodes 100 a and 100 b implanted in thepatient's skull at spaced-apart locations. FIGS. 23-26 illustratealternative arrays that may be useful in other embodiments. In FIG. 23,the array 1010 a includes four electrodes 100 arranged in a rectangulararray. The array 1010 b of FIG. 24 includes sixteen electrodes 100, alsoarranged in a rectangular array. The array 1010 c shown in FIG. 25includes nine electrodes 100 arranged in a radial array. FIG. 26illustrates an array 1010 d that includes four electrodes100.times.arranged in a rectangular pattern and a fifth electrode 100 yat a location spaced from the other four electrodes 100 x. In using suchan array, the four proximate electrodes 100.times.may be provided withthe same polarity and the fifth electrode 100 y may have a differentpolarity. In some embodiments, the housing (1052 in FIG. 19) of thepulse system 1050 may serve the function of the fifth electrode 100 y.The precise shape, size, and location of the array 1010 and the numberof electrodes 100 in the array 110 can be optimized to meet therequirements of any particular application.

One or more electrodes 100 of arrays 1010 such as those described hereinmay be provided with electrical signals in a variety of spatially and/ortemporally different manners. In some circumstances, one electrode 100or a subset of the electrodes 100 may have one electrical potential anda different electrode 100 or subset of the electrodes 100 (or, in someembodiments, the housing 1052 of the pulse system 1050) may have adifferent electrical potential. U.S. patent application Ser. No.09/978,134, entitled “Systems and Methods for Automatically OptimizingStimulus Parameters and Electrode Configurations for Neuro-Stimulators”and filed 15 Oct. 2001 (the entirety of which is incorporated herein byreference), suggests ways for optimizing the control of the electricalpulses delivered to the electrodes 100 in an array 1010. The methods andapparatus disclosed therein may be used to automatically determine theconfiguration of therapy electrodes and/or the parameters for thestimulus to treat or otherwise effectuate a change in neural function ofa patient.

In general, neural stimulation efficiency and/or efficacy may beinfluenced by an extent to and/or manner in which neural stimulationreaches and/or travels into and/or through target neural structuresand/or a target neural population, which may be affected by stimulationsignal polarity, electrode configuration, and/or electrical contactconfiguration considerations. The particular neural structures and/orneural populations targeted at any time in a neural stimulationsituation, and hence such considerations, may depend upon the nature,severity, and/or spatial boundaries of a patient's neurologicdysfunction.

Various embodiments in accordance with the present invention may beconfigured to provide bipolar and/or unipolar stimulation at one or moretimes. Neural stimulation in which both an anode and a cathode arepositioned, located, or situated within, essentially across, orproximate to a stimulation site may be defined as bipolar stimulation.Neural stimulation in which one of an anode and a cathode is positioned,located, or situated within or proximate to a stimulation site while arespective corresponding cathode or anode is positioned, located, orsituated remote from the stimulation site to provide electricalcontinuity may be defined as unipolar, monopolar, or isopolarstimulation. Unipolar stimulation may alternatively or additionally becharacterized by a biasing configuration in which an anode and a cathodeare positioned, located, or situated in different neurofunctional areasor functionally distinct anatomical regions. Those skilled in the artwill understand that an anode and a cathode may be defined in accordancewith a first phase polarity of a biphasic or polyphasic signal.

In a unipolar configuration, a pulse system 1050 may apply an identicalpolarity signal to each electrode or electrical contact positioned uponor proximate to one or more stimulation sites. Unipolar stimulation maybe defined as anodal unipolar stimulation when an anode is positionedupon or proximate to a stimulation site or a target neural population;and as cathodal unipolar stimulation when a cathode is positioned uponor proximate to a stimulation site or a target neural population.

In various situations, neural stimulation having particular stimulationsignal and/or spatial and/or temporal characteristics (e.g., bipolarstimulation, cathodal or anodal unipolar stimulation, mixed-polaritystimulation, varying duty cycle stimulation, varying frequencystimulation, varying amplitude stimulation, spatially or topographicallyvarying stimulation, theta burst stimulation, and/or other types ofstimulation applied or delivered in a predetermined, pseudo-random,and/or aperiodic manner at one or more times and/or locations), possiblyin association or conjunction with one or more adjunctive or synergistictherapies, may facilitate enhanced symptomatic relief and/or at leastpartial recovery from neurologic dysfunction.

An adjunctive or synergistic therapy may comprise a behavioral therapysuch as a physical therapy activity, a movement and/or balance exercise,an activity of daily living (ADL), a vision exercise, a reading task, aspeech task, a memory or concentration task, a visualization orimagination exercise, an auditory activity, an olfactory activity, arelaxation activity, and/or another type of behavior, task, or activity;a drug or chemical substance therapy; and/or another therapy that may berelevant to a patient's functional state, development, and/or recovery.

Neurologic dysfunction to which various embodiments of the presentinvention may be directed may correspond to, for example, motor,sensory, language, visual, cognitive, neuropsychiatric, auditory, and/orother types of deficits or symptoms associated with stroke, traumaticbrain injury, cerebral palsy, Multiple Sclerosis, Parkinson's Disease,essential tremor, a memory disorder, dementia, Alzheimer's disease,depression, bipolar disorder, anxiety, obsessive/compulsive disorder,Post Traumatic Stress Disorder, an eating disorder, schizophrenia,Tourette's Syndrome, Attention Deficit Disorder, a drug addiction,autism, epilepsy, a sleep disorder, a hearing disorder, and/or one ormore other states, conditions, and/or disorders. Depending uponembodiment details and/or the nature of a patient's neurologicdysfunction, at least partial symptomatic relief, functional recovery,and/or functional development may occur through mechanisms correspondingor analogous to Long Term Potentiation (LTP), Long Term Depression(LTD), neuroplastic change, and/or compensatory processes.

FIG. 32 is a schematic illustration of an exemplary implantationconfiguration for a neural stimulation system 1000 according to anembodiment of the invention. In one embodiment, a neural stimulationsystem 1000 may comprise a set of intracranial electrodes 100 c and 100d coupled by lead wires 124 c and 124 d to a pulse system 1050. Theintracranial electrodes 100 c and 100 d may be surgically implanted ator relative to a set of target sites, and the pulse system 1050 may beimplanted beneath the scalp 30 and adjacent to and/or partially withinthe skull 10. In certain configurations, a particular separation betweenand/or relative positioning of two or more intracranial electrodes 100 cand 100 d may be established, such that target electrode implantation orstimulation sites may correspond to anatomically remote and/or distinctregions. This may facilitate unipolar stimulation and/or stimulation ofneural populations in different neural association areas, for example,different neurofunctional areas associated with motor skills orabilities; neurofunctional areas associated with motor and languageskills; and/or neurofunctional areas associated with other skills.

FIG. 33 is a schematic illustration of another exemplary implantationconfiguration for a neural stimulation system 1000 according to anembodiment of the invention. Relative to FIG. 32, like reference numbersmay indicate like, corresponding, and/or analogous elements. As in FIG.32, a set of intracranial electrodes 100 e and 100 f may be implanted orpositioned relative to particular neurofunctional areas. In oneembodiment, the set of electrodes 100 e and 100 f may exhibit multipletypes of electrical contact configurations, orientations, and/orgeometries. For example, a particular electrode 100 e may carry anelectrical contact C_(e) that is distinctly different from one or morecontacts C_(f) carried by another electrode 100 f. Depending uponembodiment details, differences in contact configuration may facilitateestablishment of particular types of electric field distributions, whichmay influence neural stimulation efficiency and/or efficacy.

Various portions of the discussion herein focus on use of intracranialelectrodes (e.g., electrodes 100, 150, 200, 250, 300, 350, 400, 450,475, 500, 550, or 600) in neurostimulation systems. In certainalternative applications, intracranial electrodes may additionally oralternatively be used to monitor electrical potentials, for example, insituations involving electroencephalography or electrocorticography. Asuitable electroencephalograph may incorporate a system similar to theneurostimulation system 1000 shown in FIG. 19, but a sensing unit (notshown) may be used in place of the pulse system 1050. Suitablecomponents for such a sensing unit are known to those skilled in the artof electroencephalography.

FIG. 34A illustrates an intracranial electrode system 900 in accordancewith an embodiment of the invention. In one embodiment, the electrodesystem 900 comprises an electrical energy transfer mechanism (ETM) 910externally placed adjacent to a patient's scalp 30 to couple electricalenergy from a pulse generator 1050 to an intracranial electrode 920. Alead wire 915 may couple the ETM 910 to the pulse generator 1050. Thepulse generator 1050 may be of an identical, essentially identical,analogous, or different type relative to a pulse generator 1050 shown inFIGS. 19-21.

In some embodiments, the ETM 910 may comprise a conventional adhesivepatch electrode commonly used for providing an electrical coupling to aparticular location on a patient. The intracranial electrode 920 maycomprise a head 922 coupled to a shaft 924. The head 922 and shaft 924may be integrally formed of an electrically conductive material forminga conductive core 925 that forms an electrical energy conduit. Theconductive core 925 may extend throughout a portion or along the entirelength of the electrode 920. The conductive core 925 may be carried byor encased in an electrically insulating material or cladding 921. Theconductive core 925 may extend from an upper or proximal contact surface925 a to a lower or distal contact surface 925 b. Contact surfaces 925 aand 925 b provide a signal exchange interface of the conductive core925. The conductive core 925 and the insulating material 921 may vary inproportionate dimensions with one another accordingly.

FIG. 34B is a cross sectional illustration of an ETM 910 according to anembodiment of the invention. In one embodiment, the ETM 910 comprises anenergy transfer patch 912 that may have several layers. In general, anETM 910 may comprise an outer flexible, insulating, and/or articulatedlayer 916, an electrically conductive layer 914, and a gel layer 912.The conductive layer 914 may be comprised of a conductive material, suchas aluminum for example, for carrying or conveying an electrical signal.The conductive layer 914 may be appropriately shaped (e.g., oval orelliptical) for conforming to a portion of the skull's rounded surface,and may be coupled to the lead wire 915. The conductive layer 914 formsa portion of a conductive circuit between the lead wire 915 and theconductive core 925 (FIG. 34A).

The outer layer 916 may be comprised of essentially any appropriateinsulating nonconductive material as is known in the art (e.g., foam).The outer layer 916 may be smooth and flexible to facilitate contouringto the patient's skin surface 30. The gel layer 912, which may be placedin contact with scalp 30, may comprise one or more of an electricallyconductive coupling gel 912 a (such as a hydrogel or wet gel), anadhesive gel 912 b, and/or an anesthetic gel 912 c. Electrical couplinggel 912 a may be comprised of a saline composition for enhancingelectrical conductivity and decreasing losses between the conductivelayer 914 and scalp 30. The adhesive gel 912 b aids in keeping the ETM910 in place. An anesthetic gel 912 c may be incorporated to possiblyreduce or retard sensations that may result from the transfer ofelectrical signals from the ETM 910 through scalp tissues 30 to theelectrode 920.

FIG. 35 illustrates yet another embodiment of portions of anintracranial electrode system 900. In one embodiment, an intracranialelectrode 930 comprises a head 932 and a shaft 934 forming a body of theelectrode 930. The electrode 930 may contain a conductive core 925having contact surfaces 935 a and 935 b for conducting electrical energythrough the scalp 30 to a stimulation site such as the dura 20. Theconductive core 935 may be clad with an electrically insulating material931. A portion of the insulating material 931 may form one or moreportions of the shaft 934, which may contain threads 935 for tappinginto the cancellous 18. As in certain previous embodiments havingthreads, intracranial electrode 930 may be tapped into the skull 10 to adesired depth. A bore, notch or groove 933 may be formed in a proximalportion of the head 932 to facilitate tapping the electrode 930 intoplace.

FIG. 36 is an illustration of an intracranial electrode system 900according to an embodiment of the invention. A set of intracranialelectrodes 920 (shown as electrodes 920 a and 920 b) may be implantedrelative to one or more target sites within cancellous 18. For purposesof simplicity, only two electrodes 920 are shown; however, it is to beappreciated that additional or fewer electrodes 920 may be employed. Insome embodiments, ETMs 910 (shown as ETMs 910 a, 910 b) may be placedproximate to each electrode 920 a and 920 b, external to the body andadjacent the scalp 30. Such a set of ETMs 910 may be coupled to thepulse generator 1050 via leads 915 a and 915 b. Depending uponembodiment details and/or a type of neurologic dysfunction underconsideration, the intracranial electrode system 900 may be configuredto provide bipolar stimulation, as a first electrode 920 a may have afirst polarity and a second electrode 920 b may have an opposingpolarity as determined by electrical signals transmitted viacorresponding lead wires 915 a and 915 b, respectively. Alternatively,each of the electrodes 920 may be biased with the same polarity in aunipolar configuration. In such a situation, a return electrode (notshown) may be placed in another location upon the patient's body; or oneor more portions of the pulse generator's case may serve as a returnelectrode. The leads 915 a, 915 b can be generally continuous (e.g.,they can extend from the corresponding ETM 910 a, 910 b to the pulsegenerator 1050 without a break, except for an optional releasableconnection at the pulse generator 1050).

FIG. 37 is an illustration of a set of implanted intracranial electrodes940 a and 940 b according to an embodiment of the invention. In oneembodiment, the intracranial electrodes 940 a and 940 b may compriseheads 942 a and 942 b that are eccentrically offset relative to a centeraxis A1 and A2 of an electrode shaft 944 a and 944 b, respectively. Afirst offset may be defined for a first electrode 940 a by a firstradius L1 and a second radius R1, where L1>R1. Likewise, a second offsetmay be defined for a second electrode 940 b having a head 942 b withradii L2 and R2 where R2>L2. The offset radii may facilitate theplacement of intracranial electrodes 940 a and 940 b in close orgenerally close proximity to one another at a distance D, while keepingD at a minimum due to the shorter radii R1 and L2. The offset radiiprovide maximum distancing between the ETMs 910 a and 910 b. In asituation wherein several sets of electrodes may be needed fortreatment, having electrodes with off center heads 942 a and 942 b mayprovide better and/or more placement options when a plurality ofelectrodes are to be placed in close proximity to one another. Althougha set of two intracranial electrodes 940 a and 940 b are shown, it is tobe understood that larger sets may be employed depending on electrodedimensions and/or a number of stimulation sites under consideration. Inany of these embodiments, the electrodes 940 a, 940 b can be securedrelative to the skull 10 by inserting each of the electrodes 940 a, 940b into a corresponding collar, e.g., a collar 540 generally similar tothat described above with reference to FIG. 14. The collar can besecured to the skull with one or more securement elements (e.g.,threads).

FIG. 38 illustrates an intracranial electrode 950 according to anotherembodiment of the invention. In one aspect of this embodiment, electrode950 comprises a body formed of a head 952 and shaft 954, wherein thehead 952 and the shaft 954 are formed with an obtuse angle .theta. attheir juncture. The obtuse angle .theta. provides the body of theelectrode with a tapered, frustoconical shape that facilitates a morecontoured, conformal implant within the cancellous 18. The head 952 mayalso be formed with a protrusion or protruded upper portion E. Theprotrusion E may be rounded for a more contoured abutment with scalptissues 30 to enhance patient comfort. The head 952 may be contouredand/or tapered, and may be at least partially recessed within the skull10 to facilitate a more conformal positioning within the patient's skull10. Furthermore, a recessed, contoured placement within the skull 10 mayprovide a more aesthetically pleasing implant.

An outer portion of the electrode 950 may be comprised of an insulatingcladding 956 disposed around a conductive core 955. The conductive core955 can include a first electrical contact portion 955 a and a secondconductive contact portion 955 b. It is to be appreciated by those ofordinary skill in the art that the cladding 956 may be comprised of anysuitable biocompatible electrically insulating material, such as, butnot limited to, polymers and/or ceramic materials. The cladding 956 maycontain a plurality of pores 957. Pores 957 may encourage boneregeneration within and about the pores for a more friction enhancedand/or lasting placement within the skull 10. In lieu of pores 957, anexterior portion of the cladding 956 in contact with body tissues mayalso be formed with a roughened surface (not shown) that may encouragebone growth and/or regeneration. Such enhanced friction and intergrowthbetween the cladding 956 and the cancellous 18 may provide for a moresecure and/or conformal placement, which may reduce or minimizepositional migration of the implanted electrodes 950. Other embodiments(not shown) may include variations of the cladding 957 havingcombinations of compatible insulative materials comprising the exterior,such as for example, an upper proximal portion of the cladding 967 beingcomprised of a ring-like polymer insulator; and/or a distal or generallydistal portion of the cladding 967 being comprised of a ceramicinsulator.

FIG. 39 illustrates yet another intracranial electrode 960 according toan embodiment of the invention. In one embodiment, the intracranialelectrode 960 comprises a body having a head 962 and a shaft 964. One ormore portions of the head 962 and/or the shaft 964 may form a taperedtransition region, such that a juncture of the head 962 and the shaft964 form an obtuse angle 0. The intracranial electrode 960 may besurgically implanted within a patient's skull 10 such that a proximalportion (e.g., an end surface) of the head 962 is flush or substantiallyflush with an outer portion or layer 12 of the skull 10. The entirety ofthe electrode 960 may be countersunk into a recess formed through theouter skull 12 and cancellous 18.

The intracranial electrode 960 may also comprise a cladding 966surrounding a conductive core 965. The cladding 966, comprised of anysuitable biocompatible material, may in some embodiments includerecesses 967 which may encourage surrounding cancellous tissue 18 togrow within and/or around the recesses 967, thus forming an enhancedbonding between the implanted electrode 960 and the skull 10. Thismodified bonding may discourage migration of the electrode 960.

FIG. 40 illustrates an intracranial electrode system 900 according toanother embodiment of the invention. In one aspect of this embodiment,the intracranial electrode system 900 comprises at least oneintracranial electrode 970 that includes a radio frequencyidentification (RFID) element, tag, or transponder 971 and/or anothertype of proximity sensing and/or detecting device. The RFID element 971may be embedded within or carried by a portion of the head 972 and/orshaft 974, for example, within an insulating non-conductive material 973forming a portion of the head 972. Insulating material 973 mayelectrically insulate the RFID element 971 from a conductive core 975.The conductive core 975 may include contact surface areas 975 a and 975b that couple to and/or comprise a portion of an electrical conduit thatfacilitates signal transfer or electrical communication between an ETM910 and intended target tissues. The ETM 910 is electrically coupled toa pulse generator 1050. In this embodiment, the pulse generator 1050 mayinclude an RFID unit 1063 comprising an RFID reader configured toidentify one or more RFID elements 971 to either allow/enable ordisallow/disable electrical signal transmissions to particularintracranial electrodes 970 at one or more times.

The RFID unit 1063 may comprise an RFID reader that may include atransmitter and a receive module, a control unit, and a coupling element(e.g., an antenna). The reader may have three functions: energizing,demodulating, and decoding. In addition, a reader can include or befitted with an interface that converts RF signals returned from an RFIDelement 971 into a form that can be passed on to and/or processed byother elements (e.g., a controller 1060) associated with the system 900.

The RFID element 971 may comprise an integrated circuit that isactivated when placed in a transmitting field of the RFID unit 1063. Thetransmitting field may vary depending on specifications of the RFIDelement 971 and/or RFID unit 1063. When an ETM 910 is placed proximateto the intracranial electrode 970, the RFID unit 1063 may emit an RFsignal that may used to power up the electrode's RFID element 971. Inone embodiment, in the event that an RFID element 971 corresponds to orprovides a particular code and/or other information, electrical signaltransmission between the pulse generator 1050 and the ETM 910, and henceto the electrode 970, may be allowed. Such an embodiment may facilitateenhanced security neural stimulation.

The above descriptions of embodiments of the invention are notexhaustive and it is to be appreciated that, although not detailed inevery instance, certain characteristics of some embodiments may beapplicable to other embodiments. Various embodiments may includecharacteristics that are identical, essentially identical, or analogousto those described in relation to other embodiments. For example,regarding various embodiments of FIGS. 27-40, one or more of thefollowing may be incorporated therewith in a manner that is identical,essentially identical, and/or analogous to that described above: anadjunct sleeve may serve as an anchor surrounding an electrode asdiscussed with reference to FIG. 4B; a dielectric member may be includedwith an insulating layer as discussed with reference to FIGS. 3A, 4A,and 14; one or more mechanisms for adjusting the overall length of theelectrode as discussed with reference to FIGS. 6-13 may be included; anelectrode may have a compressible retaining collar as discussed withreference to FIG. 14; an electrode may have a sharper contact surface asdiscussed with reference to FIGS. 14 and 15; and/or the second electrode820 of the intracranial electrode system of FIGS. 30 and 31 may have agimbal type fitting, as discussed with reference to FIG. 18.

D. Methods

As noted above, other embodiments of the invention provide methods ofimplanting an intracranial electrode and/or methods of installing aneurostimulation system including an implantable intracranial electrode.In the following discussion, reference is made to the particularintracranial electrode 100 illustrated in FIGS. 2A-B and to theneurostimulation system 1000 shown in FIG. 19. It should be understood,though, that reference to this particular embodiment is solely forpurposes of illustration and that the methods outlined below are notlimited to any particular apparatus shown in the drawings or discussedin detail above.

As noted above, implanting conventional cortical electrodes typicallyrequires a full craniotomy under general anesthesia to remove arelatively large (e.g., thumbnail-sized or larger) window in the skull.Craniotomies are performed under a general anesthetic and subject thepatient to increased chances of infection.

In accordance with one embodiment of the present invention, however, thediameter of the electrode shaft 110 is sufficiently small to permitimplantation under local anesthetic without requiring a craniotomy. Inthis embodiment, a relatively small (e.g., 4 mm or smaller) pilot holemay be formed through at least part of the thickness of the patient'sskull adjacent a selected stimulation or monitoring site of the brain.When implanting the electrode 100 of FIGS. 2A-B, it may be advantageousto extend the pilot hole through the entire thickness of the skull. Careshould be taken to avoid undue trauma to the brain in forming the pilothole. In one embodiment, an initial estimate of skull thickness can bemade from MRI, CT, or other imaging information. A hand-held drill maybe used to form a bore shallow enough to avoid extending through theentire skull. A stylus may be inserted into the pilot hole to confirmthat it strikes relatively rigid bone. The drill may then be used todeepen the pilot hole in small increments, checking with the stylusafter each increment to detect when the hole passes through thethickness of the inner cortex 14 of the skull 10. If so desired, thestylus may be graduated to allow a physician to measure the distance tothe springy dura mater and this information can be used to select anelectrode 100 of appropriate length or, if an adjustable-lengthelectrode (e.g., electrode 300 of FIGS. 6A-B) is used, to adjust theelectrode to an appropriate length.

The location of the pilot hole (and, ultimately the electrode 100received therein) can be selected in a variety of fashions. U.S. PatentApplication Publication No. US 2002/0087201 and U.S. application Ser.No. 09/978,134 (both of which are incorporated hereinabove), forexample, suggest approaches for selecting an appropriate stimulationsite. When the desired site has been identified, the physician can borethe pilot hole to guide the contact surface 115 of the electrode 100 tothat site. In one embodiment, the physician may use anatomicallandmarks, e.g., cranial landmarks such as the bregma or the sagittalsuture, to guide placement and orientation of the pilot hole. In anotherembodiment, a surgical navigation system may be employed to inform thephysician during the procedure. Briefly, such systems may employreal-time imaging and/or proximity detection to guide a physician inplacing the pilot hole and in placing the electrode 100 in the pilothole. In some systems, fiducials are positioned on the patient's scalpor skull prior to imaging and those fiducials are used as referencepoints in subsequent implantation. In other systems, real-time MRI orthe like may be employed instead of or in conjunction with suchfiducials. A number of suitable navigation systems are commerciallyavailable, such as the STEALTHSTATION TREON TGS sold by MedtronicSurgical Navigation Technologies of Louisville, Colo., US.

Once the pilot hole is formed, the threaded electrode 100 may beadvanced along the pilot hole until the contact surface 115 electricallycontacts a desired portion of the patient's brain. If the electrode 100is intended to be positioned epidurally, this may comprise relativelyatraumatically contacting the dura mater 20; if the electrode is tocontact a site on the cerebral cortex, the electrode will be advanced toextend through the dura mater. The electrodes 100 may also be implantedto a selected depth within the cerebral cortex or at a deeper locationin the brain.

In one embodiment, the length of the electrode 100 is selected (oradjusted for electrode 300, for example) to achieve the desired level ofcontact and the electrode will be advanced until a known relationshipwith the skull is achieved, e.g., when the head 102 compresses thecontact ring 122 of the lead 120 against the exterior of the skull 10.In another embodiment, the thickness of the skull 10 need not be knownto any significant accuracy before the electrode 100 is implanted.Instead, the electrode 100 may be connected, e.g., via the lead 120, toan impedance monitor and the impedance may be monitored as the electrode100 is being implanted. It is anticipated that the measured impedancewill change when the electrode 100 contacts the dura mater 20. Once thiscontact is detected, the physician may advance the electrode a small,fixed distance to ensure reliable electrical contact over time.

As noted above, the electrode 100 may be coupled to a lead 120. Thetiming of this coupling may vary with the nature of the coupling. For alead 120 employing a contact ring 122 or the like positioned below thehead 102, the lead may be coupled to the electrode before the electrodeis introduced into the skull. In other embodiments, the lead (e.g., lead160 of FIGS. 3A-B) may be coupled to the electrode after the electrodeis properly positioned with respect to the selected site of the brain.The lead, or at least a length thereof, may be implanted subcutaneously,e.g., by guiding it through a tunnel formed between the implant site andthe intended site of a subclavicularly implanted pulse system 1050. Thepatient's scalp may then be closed over the head 102 of the electrode100 so the electrode is completely enclosed. This can materially improvepatient comfort compared to more conventional systems wherein epilepsymonitoring electrodes or the like extend through the scalp to anextracorporeal connection.

Additionally or alternatively, implant depth may be measured, estimated,or indicated through the use of a depth measurement device or apparatus.FIG. 41 is a schematic illustration of a depth measurement apparatus 175(e.g., a depth acquisition stick or DAS) and a set of intracranialelectrodes I₁-I₄. In one embodiment, an appropriate electrode length maybe determined by performing a depth measurement procedure using thedevice 175. The device 175 may be inserted into a surgically formedpilot hole 11. The device 175 may contain indicia comprising a pluralityof calibrated indicators d1-d4, which provide linear measurements as tothe depth of the pilot hole 11. The device 175 may have a retainer cuffand/or sleeve 176 that aids in keeping the device 175 in an uprightposition for accurate depth measurements.

Depending on the depth of the pilot hole 11, intracranial electrodes11-14 may have shafts of varying lengths S_(f)-S₄ that correspond to thedemarcated indicators d₁-d₄. For example, the shaft of intracranialelectrode I₁, may have a length S₁ associated with a distance d,indicated on the device 175. Likewise, intracranial electrodes I₂, I₃and I₄ may be associated with distances d₂, d₃, and d₄, respectively.The depths of the pilot holes 11 may vary from patient to patientdepending on such variables as the age of the patient and/or an implantlocation in the skull 10.

FIG. 42 is a flowchart illustrating a depth acquisition procedure 2000according to an embodiment of the invention. In one embodiment, a depthacquisition procedure 2000 may comprise an accessing procedure 2010 thatinvolves surgically accessing an implantation or stimulation site. Anaccessing procedure may utilize a surgical navigational system and/oranatomical landmarks, as discussed above, to aid in making a pilot hole11 in one or more appropriate locations. The depth acquisition procedure2000 may further comprise an insertion procedure 2020 that may involveinsertion of a depth acquisition apparatus such as device 175 (FIG. 41)into a pilot hole 11. As discussed above, the device 175 may be providedwith indicia corresponding to demarcations or units of length (e.g.,millimeters). The depth acquisition procedure 2000 may additionallycomprise a measurement procedure 2030 that involves measuring orcomparing the depth of a hole 11 relative to a calibrated indicia on ameasurement device, e.g., the device 175. As discussed above, the device17D may have calibrations corresponding to a set of shaft lengths of aseries of electrodes. The depth acquisition procedure 2000 may alsocomprise a mapping procedure 2040 that involves mapping or correlating ameasurement depth associated with a pilot hole 11 to a correspondingelectrode, for example, one of intracranial electrodes I₁-I₄. A depthacquisition procedure 2000 may additionally comprise a selectionprocedure 2050 that involves selecting an electrode characterized by anappropriate length or dimension for implantation.

Once an electrode 100 is in place, an electrical stimulus may bedelivered from a pulse system 1050 to the patient's brain via a lead 120and the electrode 100. In certain embodiments of the invention discussedpreviously, a plurality of electrodes 100 may be implanted in an array(e.g., array 1010, 1010 a, 1010 b, or 1010 c) in the patient's skull andeach of the electrodes 100 may be coupled to the pulse system 1050 by anelectrically separate lead 120. The precise nature of the stimulusdelivered via the electrode(s) 100 can be varied as desired to diagnoseor treat a variety of conditions. The type, pattern, and/or frequency ofstimulus may be selected in a manner identical, essentially identical,or analogous to or different from that outlined in U.S. Pat. No.7,010,351, for example, and/or may be optimized in a manner described inU.S. application Ser. No. 09/978,134.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense, that is to say, in a sense of “including,but not limited to.” Words using the singular or plural number alsoinclude the plural or singular number, respectively. When the claims usethe word “or” in reference to a list of two or more items, that wordcovers all of the following interpretations of the word: any of theitems in the list, all of the items in the list, and any combination ofthe items in the list.

The above-detailed descriptions of embodiments of the invention are notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example,whereas steps are presented in a given order, alternative embodimentsmay perform steps in a different order. Aspects of the inventiondescribed in the context of particular embodiments can be combined oreliminated in other embodiments.

In general, the terms used in the following claims should not beconstrued to limit the invention to the specific embodiments disclosedin the specification, unless the above-detailed description explicitlydefines such terms. While certain aspects of the invention are presentedbelow in certain claim forms, the inventors contemplate the variousaspects of the invention in any number of claim forms. Accordingly, theinventors reserve the right to add additional claims after filing theapplication to pursue such additional claim forms for other aspects ofthe invention.

What is claimed:
 1. A device for delivering electrical signals to atleast a portion of a brain of a patient, comprising: an electrode, theentire electrode being made of electrically conductive material and thusthe electrode being electrically conductive, the electrode beinggenerally a “T” shaped electrode; an electrically insulating material atleast substantially clad about the electrode; the electrode having ahead and a shaft, the head to be positioned adjacent to an outer portionof the skull of the patient, the head for stabilizing the shaft relativeto the skull; the head of the electrode having a top portion and abottom portion, with the bottom portion being contoured to substantiallymatch the contour of the portion of the skull of the patient proximateto where the electrode is inserted into a hole of the skull of thepatient; the shaft extending from the head with a first end distal thehead, at least a first electrical contact positioned at the first end ofthe shaft, the shaft for insertion into the hole of the skull of thepatient such that the electrical contact at the first end of the shaftis positioned adjacent to and in electrical contact with the surface ofthe brain of the patient, wherein the electrode can transmit electricalsignals received from an external controller electrically connected tothe head of the electrode to the brain of the patient.
 2. The device asrecited in claim 1, wherein the electrically insulating material isbiocompatible.
 3. A brain stimulating electrode, comprising: a body, theentire body being made of electrically conductive material and thus thebody being electrically conductive; an electrically insulating materialat least substantially clad about the body; the body having a head and ashaft, the head to be positioned adjacent to an outer portion of theskull of the patient, the head for stabilizing the shaft relative to theskull; the head having a top portion and a bottom portion, with thebottom portion being contoured to substantially match the contour of theportion of the skull of the patient proximate to where the body isinserted into a hole of the skull of the patient; and the shaftextending from the head with a first end distal the head, at least afirst electrical contact positioned at the first end of the shaft, theshaft for insertion into the hole of the skull of the patient such thatthe electrical contact at the first end of the shaft is positionedadjacent to and in electrical contact with the surface of the brain ofthe patient, wherein the electrode can transmit electrical signalsreceived from an external controller electrically connected to the headof the electrode to the brain of the patient.
 4. The brain stimulatingelectrode as recited in claim 3, wherein the body is generally “T”shaped.
 5. The brain stimulating electrode as recited in claim 3,wherein the electrically insulating material is biocompatible.